Fix #139: drop unsafe-inline from script-src and style-src (#139)

- Move all inline <script> blocks (layout head/theme, topbar dark toggle,
  foot, paste, new, history, mine, settings, admin, unlock) to external
  files under internal/web/static/. Page data reaches scripts via data-*
  attributes (data-paste-id, data-default-dark) instead of template vars.
- Replace inline onclick handlers (copy, delete, stats toggle) with
  addEventListener wiring.
- Convert inline style="" attributes to CSS utility classes; swatch
  colors are now set via CSSOM/DOM APIs instead of innerHTML strings.
- script-src/style-src are now plain 'self'; img-src data: stays for the
  SVG data-URI backgrounds. Verified with headless chromium: zero CSP
  violations on all pages in dark and light presets, theme swatches,
  admin lock, tables and paste view render correctly.

internal/web/static/admin.js

@@ -0,0 +1,74 @@
+// #99/#139: admin lock + settings panel. Key lives in sessionStorage for this visit only.
+(function () {
+  var KEY = 'palette_admin_key';
+  var keyInput = document.getElementById('admin-key');
+  var status = document.getElementById('admin-key-status');
+  var panel = document.getElementById('admin-panel');
+
+  function key() { return sessionStorage.getItem(KEY) || ''; }
+
+  function api(path, opts) {
+    opts = opts || {};
+    // allow callers to override the key header (e.g. validating a typed key, #99)
+    opts.headers = Object.assign({ 'X-Admin-Key': key() }, opts.headers || {});
+    if (opts.body) opts.headers['Content-Type'] = 'application/json';
+    return fetch(path, opts);
+  }
+
+  function loadSettings() {
+    api('/admin/api/settings').then(function (r) {
+      if (r.status !== 200) { showLock(); return; }
+      return r.json();
+    }).then(function (s) {
+      if (!s) return;
+      document.getElementById('rl-burst').value = s.rate_limit_burst;
+      document.getElementById('rl-refill').value = s.rate_limit_per_minute;
+      document.getElementById('max-content').value = s.max_content_bytes;
+      document.getElementById('default-expiry').value = s.default_expiry;
+      document.getElementById('slug-days').value = s.custom_slug_reservation_days;
+      document.getElementById('burn-window').value = s.burn_viewer_window_minutes;
+      panel.classList.remove('hidden');
+    });
+  }
+
+  function showLock() {
+    panel.classList.add('hidden');
+    sessionStorage.removeItem(KEY);
+  }
+
+  document.getElementById('admin-key-form').addEventListener('submit', function (e) {
+    e.preventDefault();
+    // #99: don't persist the key until the server accepts it
+    api('/admin/api/settings', { headers: { 'X-Admin-Key': keyInput.value } }).then(function (r) {
+      if (r.status === 200) {
+        sessionStorage.setItem(KEY, keyInput.value);
+        status.textContent = '✓';
+        keyInput.value = '';
+        loadSettings();
+      } else {
+        status.textContent = 'invalid key';
+        showLock();
+      }
+    });
+  });
+
+  document.getElementById('admin-settings-form').addEventListener('submit', function (e) {
+    e.preventDefault();
+    var body = {
+      rate_limit_burst: parseFloat(document.getElementById('rl-burst').value),
+      rate_limit_per_minute: parseFloat(document.getElementById('rl-refill').value),
+      max_content_bytes: parseInt(document.getElementById('max-content').value, 10),
+      default_expiry: document.getElementById('default-expiry').value,
+      custom_slug_reservation_days: parseInt(document.getElementById('slug-days').value, 10),
+      burn_viewer_window_minutes: parseInt(document.getElementById('burn-window').value, 10)
+    };
+    api('/admin/api/settings', { method: 'POST', body: JSON.stringify(body) }).then(function (r) {
+      document.getElementById('admin-save-status').textContent = r.status === 200 ? 'saved' : 'error';
+      if (r.status !== 200) showLock();
+    });
+  });
+
+  // #112: always show the lock on fresh load — do not auto-restore the
+  // panel from a stale sessionStorage key. The key is only written after a
+  // successful unlock (above) so in-page actions still work within this visit.
+})();